title: AgNa(VO2F2)2: a trioxovanadium fluoride with unconventional electrochemical properties.
abstract: We present structural and electrochemical analyses of a new double-wolframite compound: AgNa(VO2F2)2 or SSVOF. SSVOF is fully ordered and displays electrochemical characteristics that give insight into electrode design for energy storage beyond lithium-ion chemistries. The compound contains trioxovanadium fluoride octahedra that combine to form one-dimensional chain-like basic building units, characteristic of wolframite (NaWO4). The 1D chains are stacked to create 2D layers; the cations Ag(+) and Na(+) lie between these layers. The vanadium oxide-fluoride octahedra are ordered by the use of cations (Ag(+), Na(+)) that differ in polarizability. In the case of sodium-ion batteries, thermodynamically, the use of a sodium anode introduces a 300 mV loss in overall cell voltage as compared to a lithium anode; however, this can be counter-balanced by introduction of fluoride into the framework to raise the reduction potentials via an inductive effect. This allows sodium-ion batteries to have comparable voltages to lithium systems. With SSVOF as a baseline compound, we have identified new materials design rules for emerging sodium-ion systems that do not apply to lithium-ion systems. These strategies can be applied broadly to provide materials of interest for fundamental structural chemistry and appreciable voltages for sodium-ion electrochemistry.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208-3113, USA.
authors.forename: Martin D
authors.initials: MD
authors.lastname: Donakowski
authors.forename: Arno
authors.initials: A
authors.lastname: Görne
authors.forename: John T
authors.initials: JT
authors.lastname: Vaughey
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Poeppelmeier
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D055664:Electrochemical Techniques; D008958:Models, Molecular; D014639:Vanadium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D014639:Vanadium